The present invention relates to laser cladding and more particularly to MCrAlY coatings formed by laser surface fusion. MCrAlY coatings, where Mis a base metal of iron, cobalt, nickel or a combination thereof, are generally known in the art. MCrAlY coatings were developed for high temperature oxidation and corrosion protective applications. An ability to form a uniform protective oxide layer which retards further oxidation of the underlying metal made the coating particularly suited to applications in the aerospace industry. Due principally to the alloy's content of active elements such as yittrium and aluminum, preparation of MCrAlY coatings have been confined to high vacuum, typically prepared by physical vapor deposition (alternately referred to herein as P.V.D.) such as with an electron beam. A teaching of one such application may be found in U.S. Pat. No. Re. 27,920. Aside from the evident constraints on the workpiece size and production time, which eliminates physical vapor deposition for many applications and makes it cost prohibitive in others, P.V.D. formed MCrAlY layers require controlled high temperature (about 1700.degree. F.) heat treatment during and/or post deposition. Several such processes require an additional step of glass peening the MCrAlY layer.
A relatively new technology in metallurgical coatings has evolved with the application of high powered lasers to the industry. Generally, a workpiece to be coated is irradiated with an intense laser beam, melting a coating material onto a workpiece surface. The technique may be used to alloy the coating material with the underlying metal such as taught by U.S. Pat. No. 4,212,900, to provide a surface layer having unique properties on a common base substrate such as taught in U.S. Pat. No. 4,218,494 and Defensive Publication No. T 967,009, or utilizing the high energy density to alter surface properties of a material as taught in U.S. Pat. No. 4,122,240. A somewhat modified application uses the laser energy to melt particles of the coating material during their transit from a feedstock source to the coating workpiece. This is generally referred to in the art as "flame spraying," examples of which may be found in U.S. Pat. Nos. 3,310,423 and 4,269,868.
The use of controlled duration high intensity/power density laser irradiation provides an advantage of controlled heating of the coating material and the coating workpiece. That is, in cladding applications such as the present invention, laser cladding permits rapid and selective heating of the coating material and portion of the contiguous substrate surface while maintaining the bulk or body of the coated workpiece at a relatively reduced temperature. The technique consequently permits rapid cooling after irradiation since the bulk of the coated item is not necessarily heated to the melting point of the alloy coating.